sync: Add GetAllSyncData to sync/api

chrome/browser/sync/glue/generic_change_processor.cc

Index: chrome/browser/sync/glue/generic_change_processor.cc
diff --git a/chrome/browser/sync/glue/generic_change_processor.cc b/chrome/browser/sync/glue/generic_change_processor.cc
index c40fca28db7001fdc6ec56705b0805e586596e1b..61de688ec49b00781b3e77e54a49b86a089cb3c5 100644
--- a/chrome/browser/sync/glue/generic_change_processor.cc
+++ b/chrome/browser/sync/glue/generic_change_processor.cc
@@ -138,7 +138,7 @@ void GenericChangeProcessor::CommitChangesFromSyncModel() {
 
 syncer::SyncError GenericChangeProcessor::GetSyncDataForType(
     syncer::ModelType type,
-    syncer::SyncDataList* current_sync_data) {
+    syncer::SyncDataList* current_sync_data) const {
   DCHECK(CalledOnValidThread());
   std::string type_name = syncer::ModelTypeToString(type);
   syncer::ReadTransaction trans(FROM_HERE, share_handle());
@@ -303,6 +303,15 @@ syncer::SyncError AttemptDelete(
 
 }  // namespace
 
+syncer::SyncDataList GenericChangeProcessor::GetAllSyncData(
+    syncer::ModelType type) const {
+  // This is slow / memory intensive.  Should be used sparingly by datatypes.
+  syncer::SyncDataList data;
+  if (GetSyncDataForType(type, &data).IsSet())
+    return syncer::SyncDataList();
+  return data;
+}
+
 // WARNING: this code is sensitive to compiler optimizations. Be careful
 // modifying any code around an OnSingleDatatypeUnrecoverableError call, else
 // the compiler attempts to merge it with other calls, losing useful information